C{HD 2{B splitter operation with side draw removal of water to prevent hydrate formation

ABSTRACT

A continuous distillation process for recovering ethylene from an ethane-ethylene mixture containing small quantities of soluble water whereby hydrate formation is prevented in the distillation zone by removing a side draw at a point in the distillation zone where the dissolved water concentration is substantially at a maximum, passing this side draw through a drying zone to substantially remove the contained water, and returning the dried side draw to the distillation zone. The water concentration in the distillation zone is thus controlled and maintained below the level at which hydrate formation occurs.

United States Patent Gleich Nov. 25, 1975 [54] C SPLITTER OPERATION WITHSIDE 2.6001 ll) (1/l952 Hachmuth 62/28 DRAW REMOVAL OF WATER o 2.953905J/IJfifl (hrones et al c v l 4 55/29 2.974.102 3/l96l Williams 62/58PREVENT HYDRA FORMATION 3.485.886 l2/l969 Mitchell et iii M 62/28 [75]Inventor: Walter A. Gleich Pasadena, Tex.

[73] Assignee: Shell Oil Company, Houston. Tex.

[22] Filed: Oct. 23, I974 [21] App]. No.; 5",] [9

Related US. Application Data Primary E.ruminer-Norman Yudkoff AssistantExaminer-Frank Sever [57] ABSTRACT A continuous distillation process forrecovering ethyl- [63] Continuation in-part of Serl No. 334324, Feb 2!.l

973' abandoned ene from an ethane-ethylene mixture containing smallquantities of soluble water whereby hydrate formation [52] us Cl 62/.203/4. 55/35. is prevented in the distillation zone by removing a sidev. 55/29 draw at a point in the distillation zone where the dis- [51] hm2 F25J 3/00 solved water concentration is substantially at a maxi- [58]Field l7 mum, passing this side draw through a drying zone to 62/23 244| 7 substantially remove the contained water, and returni 5 5 ing thedried side draw t0 the distillation zone. The water concentration in thedistillation zone is thus [56] finances Cited controlled and maintainedbelow the level at which UNTED STATES PATENTS hydrate formation occurs.

2,498,806 2/1950 Hachmuth 7. 62/27 5 Claims, 2 Drawing Figures LIGHTENDS VENT m 12 78 l E TH YLE NE PRODUCT 22 l 2 ETHANE-ETHYLENECONTAINING FRACTION 28 E THANE AND HEA V/ E R H YDROCARBONS U.S. PatentNov. 25, 1975 3,921,41 1

77 LIGHT 72 1 l ETH YLENE 79 PRODUCT 2 ETHANE-ETHYLENE CONTAININGFRACTION 28 ETHANE AND HEAV/ER HYDROCARBONS 55 EIGHT N05 ETHYLENTE P u56 ROD c 1 P 62 x 43 58 E THA NE ETHYLENE 60 CONTAINING FRACTION 63 ETHANE AND HEAV/ER HYDROCARBONS C- SPLITTER OPERATION WITH SIDE DRAWREMOVAL OF WATER TO PREVENT HYDRATE FORMATION This application is acontinuation in-part of applicants copending application Ser. No.334.324, filed Feb. 21, 1973. now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an improved method of separating hydrocarbons. Moreparticularly, it relates to a method of separating ethylene from ethanein hydrocarbon mixtures containing soluble water in a manner such thathydrate formation is minimized or eliminated.

2. Description of the Prior Art Ethylene, an unsaturated hydrocarbon,used as a reactant in the production of a great number of products. is ahydrocarbon of great commercial importance. lt is produced by a numberof processes. For example. ethylene is produced from more saturatedhydrocarbons. e.g., by the pyrolysis of ethane or heavier hydrocarbons,such as propane, butane. naphthas. and gas oils wherein ethylene is oneof many products formed. Common to all of these processes is theproduction of ethylene in admixture with ethane and other hydrocarbons.From such mixtures ethylene is recovered in the purity required forcommercial uses by employing a number of distillation stages. There area number of processing schemes which may be employed to effect theseparation of the hydrocarbon mixture into the various fractions.

ln one processing arrangement, the hydrocarbon mixture is subjected to adistillation zone (demethanizer) wherein methane and lighter gases arerecovered as an overhead product. The bottoms from this distillationzone is then subjected to a second distillation zone (deethanizer)wherein the C and heavier hydrocarbon are recovered as a bottomsproduct. The overhead from this deethanizer, containing ethane andethylene along with a small amount of methane and C hydrocarbons, isthen subjected to a distillation zone wherein ethylene is recovered as aproduct. Such a distillation zone is referred to as a C -Splitter.

In another processing arrangement the hydrocarbon mixture is subjectedto a demethanizer to recover methane and lighter materials as anoverhead product and the bottoms from the demethanizer is feed to a Csplitter. In this C -splitter ethylene and lighter materials arerecovered as overhead products and ethane and heavier hydrocarbons arerecovered as bottoms product.

In still another processing arrangement, the hydrocarbon mixture isinitially subjected to a distillation zone (deethanizer) wherein the Cand heavier hydrocarbons are recovered as a bottoms product and theethane and lighter hydrocarbons are recovered as an overhead product.This overhead product is then fed to a demethanizer wherein methane andlighter materials are recovered as overhead products. The bottoms fromthis demethanizer, containing predominantly ethane and ethylene. is thenfed to a C- -splitter whereby ethylene is recovered as an overheadproduct. There are other possible processing arrangements which may beemployed as will be apparent to one skilled in this art. The particularprocessing arrangement employed will depend in part upon the ethylenefeedstock and the process requirements for the various fractionspresent.

Common to all of these processing arrangements is the distillation zone(C splitter) wherein the separation of ethylene and ethane is effected.This distillation generally requires refrigeration and all or a largepop tion of the distillation zone is at a temperature which is conduciveto hydrate formation.

Hydrates are insoluble solids which form as a result of reaction of freewater with hydrocarbons at low temperatures. In order for hydrates toform, water must be present as a separate phase. Therefore. in carryingout the distillation in the -splitter, the presence of free water is tobe avoided. Otherwise. the insoluble hydrates are deposited on thedistillation column trays and in the downcommers with the result thatthe column capacity and fractionation efficiency are reduced if notsubstantially impaired. Although preventive measures are incorporated inthe design of C splitter distillation systems to reduce the waterconcentration of a C splitter feed, e.g.. feed dryers are employed toremove water in the C -splitter feed down to levels as low as 0.05 ppm w1.0 ppm w there is nevertheless a problem with water accumulation in theC -splitter with consequent hydrate formation. Hydrate formation occursbecause all the water in the feed is not removed in the product streams.Water in the lower section of the column tends to distill upward fromthe bottom of the column towards the feed tray while the water in theupper section of the distillation column tends to distill downwardstoward and below the feed tray. This phenomenon causes a bulging of thesoluble water profile in the column at a point intermediate between thebottom of the column and the feed tray. The soluble water concentrationin the column continues to increase until a separate phase is formed andhydrates are produced.

There are several approaches practiced in the art for combating thisproblem, all of which are unsatisfactory due either to the impairment ofthe performance of the C -splitter or to the effect on the overallethylene recovery process. One approach the least satisfactory of all isthat of periodically shutting down the C splitter and washing the columnwith an appropriate solvent, eg an alcohol. to remove the accumulatedbydrates. This method has the disadvantage that the entire plant has tobe shut down for several days, with the ensuing loss of production. Thismethod is still employed. however, because the shortcomings of the othermethods make this one necessary on occasion.

Another method for combatting hydrate formation involves the periodicflushing of the C -splitter with an appropriate wash solution. ln thismanner a complete shut down of the C -splitter is not required; however,its operation is substantially interrupted with consequent loss ofthroughput. The flushing is effected by injecting a large slug ofalcohol or other appropriate solvent into the reflux or feed to thesplitter for a short interval of time. During this washing period, C-splitter operations are not normal. The column is typically on totalreflux and no product is being recovered. or alter natively, the columnis operated at reduced throughput during this flushing. After thewashing is completed. several hours are required to reestablish normaloperating conditions. An additional disadvantage of this method is thatthe flush solution, e.g., generally methanol. which is withdrawn withthe bottoms product can have adverse effects on downstream operations.

Still another method of dealing with the problem of hydrate formationinvolves the continuous addition of a small amount of alcohol to the(IQ-splitter. The alcohol flowing down through the column removes waterfrom the column in solution with the alcohol and is thereby removed inthe bottoms product. Although preferable to either of the precedingmethods. continuous alcohol injection has several disadvantages. In theamounts which are practical. e.g. l-Zfi by weight. the continuousalcohol addition is not very effective in preventing hydrate formation.Moreover. there is the added disadvantage of a loss of capacity for theC hydrocarbons being distilled. and the problems related to recoveringthe alcohol and reconccntrating it for reuse. Finally. there areproblems resulting from the alcohol in the ethane bottoms product. Thiscan cause problems in the downstream operations such as recycle ethanevaporization and recycle ethane pyrolysis.

Still another method for combatting hydrate formation involvesperiodically dumping the accumulated dissolved water from the system bydecreasing the bottoms temperature of the -splitter and forcingadditional ethylene and water out the bottom of the column. This methodhas the disadvantage of loss of ethylene product and results in therecycle of excessive amounts of ethylene to the pyrolysis furnaces.

It would be advantageous to have a distillation process for theseparation of ethylene from ethane and other fractions in which hydrateformation is reduced or eliminated. It would also be advantageous tohave a process for separating C fractions which provided means forpreventing the accumulation of water within the system to levels wherehydrate formation occurs. It would also be an advantage to provide aprocess for continuous operation of the C -splitter which does notrequire either the use of materials extraneous to the process in orderto prevent or control hydrate formation or operating the column underabnormal condi tions to reject water from the system.

SUMMARY OF THE INVENTION effluent stream is recycled to the distillationzone. By

this method the solubility limit of water in the hydrocarbon mixture inthe distillation zone is not exceeded. with the result that hydrateformation and ice formation do not occur.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a schematic flowdiagram of a C:- splitter process embodying a preferred modification ofthe invention.

FIG. 2 represents a schematic flow diagram of a C; splitter processembodying an alternative embodiment of the invention DESCRIPTION OF THEPREFERRED EMBODIMENTS The process according to the invention ischaracterized in that a hydrocarbon feedstock consisting primarily ofethane and ethylene with minor amounts of hy- Ill (ill

drogen. methane. acetylene. propylene. propane and dissolved water issubjected to a distillation step in which ethylene and hydrocarbons morevolatile than ethylene are recovered as overhead fractions. while ethaneand the less volatile hydrocarbons are TECU\ ered as a bottoms product.This distillation step is conducted in a distillation zone which isgenerally referred to as a -splitter. The distillation is typicallycarried out at pressures of from about psig to about 400 psig withpressures of from about 250 psig to about 350 psig being preferred. Theoptimum operating pressure will depend upon several factors. includingfeed composi tion and the degree of separation desired between ethaneand ethylene. The operating temperatures in the (T -splitter willreflect the operating pressure selected with temperatures of about (19Fin the bottoms and about l00F in the overhead being typical for 50 psigoperation and temperatures of about 50F in the bottoms and about 5F inthe overhead being typical for 400 psig operation. Operating at apreferred pressure in the range of about 250 psig to about 350 psig. theoperating temperatures will be from about 15F to about 40F in thebottoms and from about 30F to about "5F in the overhead. At theseoperating temperatures. a substantial portion of the -splitter is at atemperature conducive to hydrate formation. Therefore. the distillationis carried out so that the concentration of dissolved water in thehydrocarbon mixture being distilled does not exceed the solubility limitfor water at any point in the distillation zone. Even where thehydrocarbon feed mixture to the distillation zone is relatively dry.e.g.. containing from about 0.05 ppm w to about 3.0 ppm \v of water.which is well below the solubility limit for water in such hydrocarbonmixtures under typical operating conditions. the water neverthelesscauses problems because of the concentrating effect in the distillationzone at a point intermediate between the point at which the feed mixtureis introduced to the zone and the bottom of the zone.

In accordance with the instant invention. a side draw is removed at apoint in the zone where the dissolved water concentration issubstantially at a maximum and is passed through a drying zone wherebythe water content of the side draw is substantially reduced. Thelocation of the sidedraw relatively near the point of maximum waterconcentration is important. for if the sidedraw is located too high ortoo low in the column. hydrates eventually form in the column.Typically, the water content of the side draw after it has been dried isfrom about 0.05 ppm w to about 2.0 ppm w with a water content of fromabout 0.1 ppm w to about l.0 ppm w being preferred. The dried side drawis then returned to the distillation zone. By this procedure. the waterconcentration in the distillation zone can be maintained below thesolubility limit and ice and hydrate formation is thereby eliminated.

The point in the distillation zone at which the side draw is removed isdetermined experimentally by analyzing samples extracted from the zoneat various locations for water content. In this manner. a concentrationprofile can be established. It has been found that for a givenhydrocarbon feed composition and set of operating conditions. the pointin the zone at which the water concentration is highest remainsessentially unchanged.

The magnitude of the water concentration at that point depends upon thewater content of the feed mixture to the zone and the rate at whichwater is removed from the zone via the side d raw and the bottomsproduct.

3 With dissolved water concentrations less than about 0.0. ppm w in thehydrocarbon feed to the -splitter. the solubility limit of water in thehydrocarbon mixture will not be exceeded. Such small amounts ol waterwill pass through the column and be removed in the bottoms product.However. at dissolved water concentrations greater than about 0.05 ppm win the incoming feed to the -splitter. water will concentrate in thedistillation zone and will form a separate water phase with consequentice and hydrate formation. Therefore. the side draw removal rate must besuch that water is removed from the distillation zone at a rate at leastequal to the rate at which water enters the zone. Consequently. theamount of water being withdrawn from the zone via the side draw dryingzone must at least equal the amount of water entering the zone in thefeed. less the small amount of water leaving the zone via the bottomsstream. It is estimated that when water in excess of 0.05 ppm weight ispresent in the typical C -splitter feed at the typical operatingconditions shown in the specification that little or no water is removedwith the top product and that only about 1% to about of the waterpresent in the feed is removed with the bottoms stream. lf the rate ofremoval of water via the side draw and the bottoms stream is greaterthan the rate of input of water to the system. the water concentrationprofile in the zone will be reduced until there is again an equilibriumbetween water input and water outtake via the side draw drying zone andthe bottoms stream. It is therefore possible to select the degree ofdryness that is, the maximum water concentration for the zone byadjusting the side draw removal rate.

The side draw is either a liquid side draw or a vapor side draw.although a liquid side draw is generally preferred. With a liquid sidedraw the process requirements are simpler and the side draw dryer ismore compact.

Ideally. the side draw after it has been dried is returned to thedistillation zone at the equilibrium location. Generally, this meansthat the side draw is removed from one tray in the distillation columnand is returned to an adjacent tray. However. this need not be the case.Since the side draw removal rate is generally quite small as comparedwith the total flow through the distillation zone. the dried side drawcan be returned to the distillation zone at another point. e.g.. a pointhigher or lower in the zone. with only a minimal effect on the overallfractionation efficiency and column capacity.

The drying agent employed in the drying zones. the feed dryer ifemployed and in the side draw dryer. is any of the conventional suitabledessicants. such as bauxite, alumina. silica gel. etc.. or is amolecular sieve. which traps the contained water but allows thehydrocarbons to pass. Whatever drying agent is employed. it is generallydesirable to provide such drying agent in two drying vessels. In thismanner. it is possible to regenerate a dryer which has become saturatedwith water while continuing the operation of the dehydration of thedistillation zone on a continuous basis. However. if the distillationzone is not operating near the dissolved water solubility limit anditthe feed to the splitter is sufficiently dry. e.g.. about 2.0 ppm w.then the dryer which requires regeneration can be taken offstream andregenerated before the water concentration in the distillation zonebuilds up to undesirable levels. As a result, it is practical to operatethe -splitter with only one drying vessel.

The regeneration oi a dryer which has become satu rated with water isaccomplished in various conventional ways. some of which includeheating. gas stripping. back flushing with a water miscible solvent.etc. The method selected to regenerate the dryer will depend in partupon the drying agent utilized.

The feed to the -splitter can vary widely in composition depending uponthe choice of feedstock in the ethylene process as well as the sequenceselected to fractionate the crude ethylene-containing product into thedesired fractions. Generally. as the proportion of ethane in the Csplitter feed relative to ethylene in creases. the dissolved waterconcentration. at which the C -splitter can be continuously fed withoutthe formation of a separate water phase. also increases. Typically. withethane/ethylene ratios of from about 1:3 to about 3:1 in the C splitterfeed. aside draw dryer is required whenever the dissolved waterconcentration cs ceeds about 0.05 ppm W. In many ethylene recoverysystems. the feed to the -splitter has been previously dried to maintaina low dissolved water concentration. e.g.. from about 0.05 ppm w toabout 2.0 ppm \v. However. the process of the instant invention isapplicable whether or not the -splitter feed has been previously dried.In fact. one advantage of the instant invention is that the upstreamfeed dryer can be eliminated if the feed does not have an extremely highconcentration of dissolved water. e.g.. no more than 50 ppm w. When everan upstream Feed dryer is employed. the hydrocarbon mixture to be driedis dried either as a liquid or a gas and the flow through the dryer iseither up-l'low or down-flow. depending upon the design of the dryer.This is also true for the side draw dryer.

As mentioned previously. the feed to the C splitter contains, inaddition to ethane and ethylene. smaller quantities of hydrogen.methane. acetylene. propane and propylene. The amounts of thesematerials present in the -splitter feed will depend upon the type ofethylene process as well as the upstream processing of theethane-ethylene containing fraction prior to the C splitter. If theconcentration of hydrocarbons lighter than ethylene is very low.ethylene is recovered in a conventional manner as an overhead productfrom the C splitter. However. generally there are sutficientconcentrations of light ends present (hydrogen. methane. acetylene.etc.) such that ethylene is recovered in a pasteurizing section of thedistillation zone. This pasteurizing section. from which the ethyleneproduct is recovered. is located at a point between the feed tray andthe overhead. The exact location will depend upon the composition of thefeed to the -splitter and the ethylene purity desired.

DESCRIPTION OF THE DRAWlNGS FIGS. 1 and 2 show by way of example the Howschemes of different embodiments otthe invention. It is understood thatthere are other embodiments of the invention as will be known to thoseskilled in the art and that the invention is not to be limited to theembodiments illustrated herein. Conventional processing equipment suchas valves and the like are not illustrated as the location and nature oithese will be appar' cut to one skilled in this art.

Referring to FIG. 1, a gaseous hydrocarbon mixture consisting primarilyof ethane and ethylene with minor amounts of hydrogen. methane.acetylene. propylene. propane and water is introduced via line 2 to afeed dryer 4 or 41: wherein it is contacted with a drying agent wherebythe water content of the hydrocarbon mixture via line 54 to providereflux for the distillation. The is reduced to a level of about 0.05 ppmw to about 2.0 light ends are vented from the accumulator 53 via lineppm w. The dried hydrocarbon mixture from the feed 55. Ethylene isrecovered from a pasteurizing section in dryer is then carried via line12 to an intermediate porthe distillation zone 10 via line 56. Thethermal energy tion ol'a distillation zone 10 (C -splitter). In thedistillafor the distillation is supplied via reboiler 58 and the tionzone the hydrocarbon mixture is fractionated to bottoms productcontaining ethane and heavier hydrogive ethylene and hydrocarbons morevolatile than ethcarbons. is recovered via line 60.

ylene as an overhead product from the distillation zone The side draw isremoved from the distillation zone 10 and ethane and the less volatilehydrocarbons as a 59 via line 62. However. in this modification of theinbottoms product. The distillation is typically carried vention. theside draw removed via line 62 is combined out at pressures in the rangeof from about 250 psig to with the -splitter hydrocarbon feed mixtureofline 42 about 350 psig and the operating temperatures in the and themixture is dried in feed dryer 40 or 4011. Whendistillation zone 10 aregenerally from about -3UF to ever the side draw withdrawn via line 62 isa liquid. it is about 40F. vaporized in vaporizer 63 prior tocombination with The overhead vapor from the distillation zone l0. l5feed mixture carried via line 42. This vaporizer is omitcontainingpredominantly ethylene with small amounts ted whenever the side draw isa vapor or whenever of methane. hydrogen and ethane is carried via line13 there is sufficient superheat in the C -splitter feed mixto condenser14 wherein the ethylene and ethane are ture to vaporize the side draw.The advantage of this condensed and are collected in accumulator 16. Thearrangement is that the water removal function for light ends. e.g.hydrogen and methane. are vented 30 both the feed mixture and the sidedraw is accomfrom the accumulator 16 via line 17. The liquid fromplished with only one set of dryers. Employing this the accumulator.containing essentially ethylene and a modification of the inventiondoes. however. result in a very small amount of ethane is returned vialine 18 to small loss in fractionating capacity and efficiency due thetop of the distillation zone 10 as reflux. Ethylene is to the side drawbeing returned to the distillation zone recovered from a pasteurizingsection in the distillation 35 50 at the feed tray location instead ofnear the equilibzone 10 as reflux. Ethylene is recovered from apasteurrium position from which it was withdrawn in the zone. izingsection in the distillation zone 10 via line 19. A However. since thesize of the side draw removed via side draw is removed via line 22 at apoint in the zone line 62 is small in comparison to the feed streamcarwhere the dissolved water concentration is substanried via line 42the adverse effect on the fractionating tially at a maximum and ispassed through a dryer or efficency and column capacity is small. 200whereby the water content of the side draw is substantially reduced. Theeffluent from the drying zone is EXAMPLE I then returned via line 24 tothe distillation zone 10. The The following example illustrates theemployment of bottoms product from the distillation zone 10 containthisinvention as shown in FIG. 1. in the separation of ing ethane andheavier hydrocarbons (including small an ethane-ethylene mixturecontaining minor amounts amounts of ethylene and water) is recovered vialine of methane. propane. propylene and water. An ethane- 28. Thethermal energy required for the distillation is ethylene feed mixture isobtained from the overhead of supplied via reboiler 26 attachedconventionally to the a deethanizer employed in the recovery of gaseousbottom of the distillation zone 10. product in an ethylene process inwhich gas oil, naph- FIG. 2 represents a modification of the instantinventha and ethane feedstocks are thermally cracked to tion whereinadvantage is taken of the feed dryer to the lighter hydrocarbonproducts. The ethaneethylene C -splitter and as a result the desiredwater removal is containing feed mixture is fed at a rate of 14,171moles accomplished without a separate dryer for the side per hour totray 32 of a distillation column containing draw. The gaseoushydrocarbon feed mixture carried 124 trays.

out by line 42 is combined with the side draw carried by The column isoperated with an overhead temperaline 62 and the mixture is introducedvia line 43 to the ture of-l 8F and a bottoms temperature of 24F. Thefeed dryer 40 or 4011. The effluent from the drying zone feed mixture isintroduced as a vapor at a temperature is carried via line 44 to anintermediate portion of a disof 13F. The overhead pressure is 299 psiaand the bottillation zone 50. In the distillation zone 50, the hydrotomspressure was 312 psia. A liquid side draw is recarbon mixture isfractionated to give ethylene and hymoved from tray 19 and is passedthrough a separate drocarbons more volatile than ethylene as an overheaddryer containing mole sieves as a drying agent. The product and ethaneand the less volatile hydrocarbons dried side draw is then returned tothe column at tray as a bottoms product. The overhead vapor from thedis- [8. The following Table 1 presents the typical rates and tillationzone 50 is carried via line 51 to condenser 52 compositions of thevarious streams.

TABLE 1 Overhead Bottom Side Draw Side Draw Feed Product Product ToDryer Return Mole/Hr Mole/Hr Mole/Hr Mole/Hr Mole/Hr Methane 2.2 2.2Ethane 4139.8 3.5 4136.3 317.4 327.4 Ethylene 10000.0 9955.7 44.3 154.0154.0 Propane Propylene 29.5 29.5 Water 0 04-134 0.00042 0.04441 0.00049(P.p.m.rnolel (3.ll (0.11 (92.2) 11.0)

wherein it is partially condensed and the products col- By this method.the column is operated continuously lected in accumulator 53. The liquidproduct from the without hydrate formation and without addition ofalaccumulator 53 is returned to the distillation zone 50 cohol.

EXAMPLE 2 The following example illustrates the employment of thisinvention as shown in FIG. 2 in the separation of an ethane-ethylenemixture containing minor amounts of methane, propane, propylene. andwater. The ethaneethylene feed mixture was obtained from the overhead ofa deethanizer employed in the recovery of gaseous product in an ethyleneprocess in which a gas oil feedstock is thermally cracked to lighterhydrocarbon prod ucts.

The column was operated with an overhead temperature of -18F and abottoms temperature of 23F. The feed mixture was introduced as a vaporat a temperature of 23F. The overhead pressure was 300 psia and thebottoms pressure was 315 psia. A liquid side draw was removed from tray[9 and was passed through the feed dryer containing mole sieves as adrying agent. The dried side draw was then returned to the column attray 27. When the hydrocarbon feed mixture is fed at the rate of l2.l lmoles per hour to tray 27 of a distillation column containing 108 trays,the following data presented in Table II are typical of the rates andcompositions of the various streams.

l. in a continuous distillation process for recoxering ethylenecomprising introducing into a distillation zone a C hydrocarbon fractionconsisting essentially of ethane and ethylene and additionallycontaining from about 0.05 ppm weight to about ppm weight soluble water.the improvement which comprises:

a. removing as a side draw a portion of the hydrocarbon and water fromsaid distillation zone at a point intermediate between the point atwhich the feed mixture is introduced to said zone and the bottom of thezone;

b. passing said side draw through a drying zone; and

c. returning the effluent from said drying zone to said distillationzone. whereby the distillation zone is 5 continuously operated withoutsubstantial hydrate formation and ethane is removed as a bottoms productsubstantially free from non-hydrocarbons.

2. The process of claim 1 wherein said side draw is removed from saiddistillation zone at a point where the water concentration issubstantially a maximum.

3. The process of claim 2 wherein the water concentration of theei'fluent from said drying zone is from about 0.05 ppm weight to about 2ppm weight.

4. The process of claim I wherein the water removed By this method. acolumn was operated continuously without hydrate formation and withoutaddition of alcohoi.

I claim as my invention:

via said side draw is equal or greater than the water introduced to saiddistillation zone.

5. The process of claim I wherein the side draw from said distillationzone is combined with fresh feed to the drying zone.

1. IN A CONTINUOUS DISTILLATION PROCESS FOR RECOVERING ETHYLENECOMPRISING INTRODUCING INTO A DISTILLATION ZONE A C2 HYDROCARBONFRACTION CONSISTING ESSENTIALLY OF ETHANE AND ETHYLENE AND ADDITIONALLYCONTAINING FROM ABOUT 0.05 PPM WEIGHT TO ABOUT 50 PPM WEIGHT SOLUBLEWATER, THE IMPROVEMENT WHICH COMPRISES: A. REMOVING AS A SIDE DRAW APORTION OF THE HYDROCARBON AND WATER FROM SAID DISTILLATION ZONE AT APOINT INTERMEDIATE BETWEEN THE POINT AT WHICH THE FEED MIXTURE ISINTRODUCED TO SAID ZONE AND THE BOTTOM OF THE ZONE; B. PASSING SAID SIDEDRAW THROUGH A DRYING ZONE; AND C. RETURNING THE EFFLUENT FROM SAIDDRYING ZONE TO SAID DISTILLATION ZONE, WHEREBY THE DISTILLATION ZONE ISCONTINUOUSLY OPERATEF WITHOUT SUSUBSTANTIAL HYDRATE FORMATION AND ETHANEIS REMOVED AS A BOTTOMS PRODUCT SUBSTANTIALLY FREE FROMNON-HYDROCARBONS.
 2. The process of claim 1 wherein said side draw isremoved from said distillation zone at a point where the waterconcentration is substantially a maximum.
 3. The process of claim 2wherein the water concentration of the effluent from said drying zone isfrom about 0.05 ppm weight to about 2 ppm weight.
 4. The process ofclaim 1 wherein the water removed via said side draw is equal or greaterthan the water introduced to said distillation zone.
 5. The process ofclaim 1 wherein the side draw from said distillation zone is combinedwith fresh feed to the drying zone.